From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D8163A59 for ; Wed, 8 Jan 2025 12:46:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736340365; cv=none; b=qPZWCImfqdm4+zw0mFxf/WCaPSGkOZ1dMnrUnS5W8p+FODazSuE1Zqdo6qQScwcXf5YaMfK5xbBmgwNOkiHbYCax+0gZB9wpwPHUBZfLoSwBvfMIpWxvIrpRQpfCPTyAysDlRu/59QjaXmezv4w4OwJMZXrUcdGRiJJ3DHv2t1s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736340365; c=relaxed/simple; bh=XFn7MM9I0cO+I3IWSfb4n/NmvMNGu3wjeVGBkM4VrBI=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=ImW2DTBjWi538nxMQBa3nQxCN3QpN/mxPrloRaOqfCMHlGahPAF9D7rLSFcM0IvkrlPSYCC9tUuDvrpdTmBGQN4mKA+wlU0xAhZJqmPLAejlGR6Nt9nNEn3Aay1JYQpWKn0hTEa6vpWGznSwAclcw6szjn0qsFb5UJjo4m3TaAA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gLK59k7f; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gLK59k7f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 355D2C4CEDD; Wed, 8 Jan 2025 12:46:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736340365; bh=XFn7MM9I0cO+I3IWSfb4n/NmvMNGu3wjeVGBkM4VrBI=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=gLK59k7fLDGFHjR8+HalV2J2J7moIQPJqJjpbLS5tEI5/OoHPSL/AXy6y+xSiUPkY 5EfueZTzOWy56HWUVB0JuYccRHzeUTTS6biPJZOtAlVUhp94mz8lgOSQWvdPH8GSNz uVwOb3y3YrcpYKRXJwyFGKkZG64IFJMNOtEvqwlS6XgxQ/6GjhZWwMPzwixmwQb9B7 6kujKf6JoML7ux0h0jYD8m9nrMFr2ou46hBQs5CTUB4J6Yg69gsnHPwo54BLoVqcp5 0MWYX/vdt/pVICrLQ/tXTAgrZ5gA6sBD55F58IO7ai7aXWUsPifJvNujhm/ChCgRpB f+7L5BHqoOPOQ== Message-ID: <677e5946-3b3e-4f4a-892a-8aa8bfb3e45b@kernel.org> Date: Wed, 8 Jan 2025 20:46:00 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: chao@kernel.org, "linux-f2fs-devel@lists.sourceforge.net" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/2] f2fs: fix missing discard candidates in fstrim To: Chunhai Guo , "jaegeuk@kernel.org" References: <20250102101310.580277-1-guochunhai@vivo.com> <62b14417-1297-4ed6-9ff3-b24115d433c4@kernel.org> Content-Language: en-US From: Chao Yu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/1/3 16:07, Chunhai Guo wrote: > 在 1/3/2025 11:26 AM, Chao Yu 写道: >> On 2025/1/2 18:13, Chunhai Guo wrote: >>> fstrim may miss candidates that need to be discarded in fstrim, as shown in >>> the examples below. >>> The root cause is that when cpc->reason is set with CP_DISCARD, >>> add_discard_addrs() expects that ckpt_valid_map and cur_valid_map have been >>> synced by seg_info_to_raw_sit() [1] and tries to find the candidates based >>> on ckpt_valid_map and discard_map. However, seg_info_to_raw_sit() does not >>> actually run before f2fs_exist_trim_candidates(), which results in failure. >> Chunhai, >> >> Can you please use nodiscard option due to fstrim stopped to return >> trimmed length after below commit: >> >> 5a6154920faf ("f2fs: don't issue discard commands in online discard is on") > > Thank you for your explanation, but I guess this issue is not relevant > to this commit, and I understand that '0 B (0 bytes) trimmed' is fine. > > The real problem is that there are actually many candidates that should > be handled in fstrim, but it cannot find any of them. > > f2fs_trim_fs() >     f2fs_write_checkpoint() >         ... >         if (cpc->reason & CP_DISCARD) { >                 if (!f2fs_exist_trim_candidates(sbi, cpc)) { >                     unblock_operations(sbi); >                     goto out; // Not candidate is found here and exit. >                 } >             ... >         } > >>> root# cp testfile /f2fs_mountpoint >>> >>> root# f2fs_io fiemap 0 1 /f2fs_mountpoint/testfile >>> Fiemap: offset = 0 len = 1 >>> logical addr. physical addr. length flags >>> 0 0000000000000000 0000000406a00000 000000003d800000 00001000 >>> >>> root# rm /f2fs_mountpoint/testfile >>> >>> root# fstrim -v -o 0x406a00000 -l 1024M /f2fs_mountpoint -- no candidate is found >>> /f2fs_mountpoint: 0 B (0 bytes) trimmed >>> >>> [1] Please refer to commit d7bc2484b8d4 ("f2fs: fix small discards not to >>> issue redundantly") for the relationship between seg_info_to_raw_sit() and >>> add_discard_addrs(). >>> >>> Fixes: 25290fa5591d ("f2fs: return fs_trim if there is no candidate") >>> Signed-off-by: Chunhai Guo >>> --- >>> fs/f2fs/segment.c | 10 +++++----- >>> 1 file changed, 5 insertions(+), 5 deletions(-) >>> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>> index eade36c5ef13..8fe9f794b581 100644 >>> --- a/fs/f2fs/segment.c >>> +++ b/fs/f2fs/segment.c >>> @@ -2070,7 +2070,7 @@ static int f2fs_issue_discard(struct f2fs_sb_info *sbi, >>> } >>> >>> static bool add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc, >>> - bool check_only) >>> + bool synced, bool check_only) >>> { >>> int entries = SIT_VBLOCK_MAP_SIZE / sizeof(unsigned long); >>> struct seg_entry *se = get_seg_entry(sbi, cpc->trim_start); >>> @@ -2098,7 +2098,7 @@ static bool add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc, >>> >>> /* SIT_VBLOCK_MAP_SIZE should be multiple of sizeof(unsigned long) */ >>> for (i = 0; i < entries; i++) >>> - dmap[i] = force ? ~ckpt_map[i] & ~discard_map[i] : >>> + dmap[i] = synced ? ~ckpt_map[i] & ~discard_map[i] : >> I guess this condition "force ? ~ckpt_map[i] & ~discard_map[i]" didn't cover >> all below cases, thoughts? >> - ckpt_map[i] == 0 // write data, and then remove data before checkpoint >> - ckpt_map[i] != 0 // remove data existed in previous checkpoint > > From the handling of ckpt_valid_map in update_sit_entry(), I guess the > condition can cover both cases. > For example, when the checkpoint is enabled, all the set bits in the > ckpt_valid_map remain set before the checkpoint (even when the blocks > are deleted), which makes it find all the right bits in both cases. My point is for fstrim case, we only need to check discard_map bitmap? once bit(s) in discard_map bitmap is zero, no matter the status of bit(s) in ckpt_map bitmap, we need to trigger a checkpoit for following discard submission? Thanks, > > Thanks, > >> >> Thanks, >> >>> (cur_map[i] ^ ckpt_map[i]) & ckpt_map[i]; >>> >>> while (force || SM_I(sbi)->dcc_info->nr_discards <= >>> @@ -3275,7 +3275,7 @@ bool f2fs_exist_trim_candidates(struct f2fs_sb_info *sbi, >>> >>> down_write(&SIT_I(sbi)->sentry_lock); >>> for (; cpc->trim_start <= cpc->trim_end; cpc->trim_start++) { >>> - if (add_discard_addrs(sbi, cpc, true)) { >>> + if (add_discard_addrs(sbi, cpc, false, true)) { >>> has_candidate = true; >>> break; >>> } >>> @@ -4611,7 +4611,7 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc) >>> /* add discard candidates */ >>> if (!(cpc->reason & CP_DISCARD)) { >>> cpc->trim_start = segno; >>> - add_discard_addrs(sbi, cpc, false); >>> + add_discard_addrs(sbi, cpc, false, false); >>> } >>> >>> if (to_journal) { >>> @@ -4653,7 +4653,7 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc) >>> __u64 trim_start = cpc->trim_start; >>> >>> for (; cpc->trim_start <= cpc->trim_end; cpc->trim_start++) >>> - add_discard_addrs(sbi, cpc, false); >>> + add_discard_addrs(sbi, cpc, true, false); >>> >>> cpc->trim_start = trim_start; >>> } > >